At high edgewise flow speeds, reversed flow causes excursions in pitching moment and blade torsion on the rotor blades of helicopters and wind turbines. Our prior work has shown that a yawed fixed wing at angle of attack in reversed flow generates a sharp-edge vortex. The sharp-edge vortex is a primary feature of the flow under the rotor blade. During operation as a rotor blade at high advance ratio in a wind tunnel, stereo PIV results show that the well-formed sharp-edge vortex at 240 degrees azimuth resembles that on a forward-swept wing. This vortex stops growing before 270 degrees and convects with the blade by 300 degrees. Static pressure computed from interpolated velocity data show the effects of vortex-induced radial pressure gradient. This explains the finding of inboard-directed radial flow at 300 degrees azimuth, overcoming centrifugal effects. Viscous stress is shown to have only a minor effect on the static pressure field computation.
Dynamic Effects in the Reverse Flow Velocity Field
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Shukla, D, Hiremath, N, Raghav, V, & Komerath, N. "Dynamic Effects in the Reverse Flow Velocity Field." Proceedings of the ASME/JSME/KSME 2015 Joint Fluids Engineering Conference. Volume 1: Symposia. Seoul, South Korea. July 26–31, 2015. V001T13A002. ASME. https://doi.org/10.1115/AJKFluids2015-13545
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